In a production facility such as a semiconductor manufacturing system, a plurality of kinds of processes are executed for a substrate serving as a work. To do this, a production facility of this type requires transfer of a work between a plurality of processing apparatuses. Work transfer schemes are roughly classified into a system using an automatic guided vehicle (AGV) (e.g., Japanese Patent Laid-Open No. 2004-280213), a system using an aerial train, and a system using a permanently installed transfer unit such as a transferor belt.
On the other hand, a production facility of this type requires improvement of the transfer efficiency so as to process a number of works. Improvement of the transfer efficiency depends on the transfer routes of individual works between the plurality of processing apparatuses. Japanese Patent Laid-Open No. 2004-280213 discloses a technique related to transfer route selection for an AGV. Japanese Patent Laid-Open No. 2003-233768 describes general route searching methods (Dijkstra method and dual Dijkstra method).
In a system using an AGV or aerial train, the AGV or aerial train is temporarily occupied for transfer of a specific work. Such a system is therefore poor in capability for parallelly transferring a mass of works, as compared to a system using a permanently installed transfer unit such as a transferor belt. Additionally, individual units such as an AGV and aerial train tend to be more expensive than a permanently installed transfer unit. If the number of units is increased to improve the transfer capability, the cost of the whole system inevitably rises. Furthermore, transfer control including transfer route selection also becomes complex.
On the other hand, in the system using the permanently installed transfer unit, the transfer unit is permanently installed. For this reason, control specialized to the layout of transfer units is employed for transfer control, and the transfer control is generally determined based on the experiments of engineers (actual operational records of the transfer system in the past). However, along with the recent rapid progress of development technologies, diversified consumer needs, and shortening product lives, the production methods are switching to flexible production systems for small-size batch production. This generates demands for production facilities which allow flexible changes according to enlargement or reduction of the production scale. Regarding this point, the system using the permanently installed transfer unit needs to re-design transfer control from the beginning every time the layout of transfer units changes, or some of them are broken.